The age a child starts puberty may be related to their parents' height relative to their own, according to a new study. The research, published in the journal PLOS, suggests that this so-called "height gap" could explain both early and late onset puberty - and remove the need for unnecessary diagnostic testing.
"We found that the age a child reaches puberty is based on how the body responds to the child's individual growth needs," said co-author Dr Yehuda Limony. "When a 'tall' child seems to be exceeding a parent's height, he may begin puberty earlier than his fellow peers to slow his growth and ensure that his final adult height is in the 'target' range."
And the opposite is also true. "'Short' children don't reach puberty until later than the societal average because their bodies are giving them extra time to grow in order to reach a parent's height," Dr Limony explains.
As part of the study, researchers from Ben-Gurion University examined data from 170 Israeli children and 335 Polish children. Boys were followed from ages 8 to 18, while girls were tracked until age 17. Heights were measured periodically at different intervals of time. In addition, target heights, or the average of mum and dad's stature, were calculated, as well as the children's BMI and the age of their pubertal growth spurt. (For girls, this measure correlates with age of first period).
When they analysed the results, both height and weight emerged as important factors.
"We found an association between the onset age of puberty and two childhood parameters: body fat as represented by a standardised BMI and a child's height relative to parent's height as represented by the 'height gap'", the authors note.
The suggestion is that there might be an innate brain mechanism, something the researchers term a "somatometer" which tracks a child's growth. In a nutshell, it monitors body growth, and activates hormones to initiate puberty "in synchrony with the target adult height".
Innate brain mechanisms aside, what exactly does the research mean in real terms?
According to Dr Limony, a child who hits puberty earlier than their peers, but at a time consistent with this height gap should be considered "healthy".
"We believe that using this model, or similar ones, will reduce the use of unnecessary diagnostic procedures while also explaining the emergence of early- or late-onset puberty," he says.
According to the study authors, children who fall into these categories are often sent for testing to rule out any underlying health conditions, such as a brain tumour. "These tests, which often include magnetic resonance imaging, are expensive and cause discomfort to children and their families," they note, adding that the results usually indicate "idiopathic precocious or delayed puberty". In other words, early or late puberty isn't attributable to any particular cause.
Precocious puberty in girls, is defined by the development of breasts and pubic hair before eight years of age, or starting periods before nine years of age. For boys, it's the development of pubic hair and enlargement of genitalia before the age of nine. While early puberty is estimated to occur in four - five per cent of girls, it's far less common in boys. Conversely, puberty is said to be delayed when signs do not appear by age 13 for girls and age 14 for boys.